1. Sustantivos, articulos, y adjetivos
Matching nouns with their articles and adjectives.

2. Masculino vs. Femenino
All Spanish nouns are either masculine or feminine. This has nothing to do with the object itself and must be memorized.
Most nouns ending in “o” are masculine.
Most nouns ending in “a” are feminine.
The definite article before the word matches the gender of the word.
El – masculine, singular (el libro)
La – feminine, singular (la camisa)
Los – masculine, plural (los libros)
Las – feminine, plural (las camisas)

3. Indefinite articles
To say “a” or “some” in Spanish you use the indefinite articles below.
Un one/a…masc., sing. Un libro
Una one/a…fem., sing. Una camisa
Unos some…masc., plural Unos libros
Unas some…fem., plural Unas camisas

4. Adjective agreement
Adjectives must agree with the nouns they follow or modify. Adjectives that end in “o” have four forms.
El amigo sincero
La amiga sincera
Los amigos sinceros
Las amigas sinceras
P.S.

5. Different endings
Adjectives that end in “e” or in a consonant have only two forms – singular and plural. They don’t change from masculine to feminine.
El curso interesante los cursos interesantes
La clase interesante las clases interesantes
El curso dificil los cursos dificiles
La clase dificil las clases dificiles